The validity of the ‘General Practice Physical Activity Questionnaire’ against accelerometery in patients with chronic kidney disease

Background: The majority of patients with chronic kidney disease (CKD) are physically inactive. Simple yet accurate assessment of physical activity is important in identifying those in need of intervention. The ‘General Practice Physical Activity Questionnaire’ (GPPAQ) is a well-used clinical and research tool, but has not been validated.

Methods: Forty individuals with CKD (age 62.5 (SD: 11.1) years, estimated glomerular filtration rate (eGFR) 33.2 (SD:19.1) ml/min/1.73 m2) completed the GPPAQ and objective physical activity was measured using a GENEActiv accelerometer for 7 days. Physical activity status was grouped as ‘Active’ (i.e. meeting current physical activity UK guidelines) or ‘Inactive.’ Sensitivity and specificity were calculated. Accuracy was defined as the probability the GPPAQ could correctly classify a patient as either ‘Active’ or ‘Inactive’ (based on accelerometery).

Results: Using accelerometery, 18% of participants met the current UK guidelines, whereas 27% were classed as ‘Active’ according to GPPAQ. Sensitivity of the GPPAQ was 54.6% and specificity was 96.6%. The ‘accuracy’ of the GPPAQ was 85.0%. The accuracy of the GPPAQ was greater in males and those not in employment/retired, although these differences were not statistically significant.

Conclusions: The GPPAQ may be a useful tool to identify CKD patients who would benefit most from a physical activity intervention. In particular, the GPPAQ can accurately identify those not sufficiently active.